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Date: Tue, 12 Mar 2024 15:24:23 +0000
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From: Marc Zyngier <maz@kernel.org>
To: David Woodhouse <dwmw2@infradead.org>
Cc: linux-arm-kernel@lists.infradead.org,
	kvm@vger.kernel.org,
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	"Rafael J. Wysocki" <rafael@kernel.org>,
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Subject: Re: [RFC PATCH 0/2] Add PSCI v1.3 SYSTEM_OFF2 support for hibernation
In-Reply-To: <20240312135958.727765-1-dwmw2@infradead.org>
References: <20240312135958.727765-1-dwmw2@infradead.org>
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On Tue, 12 Mar 2024 13:51:27 +0000,
David Woodhouse <dwmw2@infradead.org> wrote:
> 
> The upcoming PSCI v1.3 specification adds support for a SYSTEM_OFF2

Pointer to the spec? Crucially, this is in the Alpha state, meaning
that it is still subject to change [1].

> function which is analogous to ACPI S4 state. This will allow hosting 
> environments to determine that a guest is hibernated rather than just 
> powered off, and ensure that they preserve the virtual environment 
> appropriately to allow the guest to resume safely (or bump the 
> hardware_signature in the FACS to trigger a clean reboot instead).
> 
> This adds support for it to KVM, and to the guest hibernate code.
> 
> Strictly, we should perhaps also allow the guest to detect PSCI v1.3, 
> but when v1.1 was added in commit 512865d83fd9 it was done 
> unconditionally, which seems wrong. Shouldn't we have a way for 
> userspace to control what gets exposed, rather than silently changing 
> the guest behaviour with newer host kernels? Should I add a 
> KVM_CAP_ARM_PSCI_VERSION?

Do you mean something like 85bd0ba1ff98?

	M.

[1] https://documentation-service.arm.com/static/65e59325837c4d065f6556a6

-- 
Without deviation from the norm, progress is not possible.